Enabling technology for the manufacture of multiple layer integrated circuit devices has been chemical mechanical planarization (CMP). In this process, each layer of wiring devices or of insulating material is polished flat (planarized) prior to deposition of the next layer. CMP facilitates the construction of multi-layer integrated circuit devices by reducing irregularities in surface topography to an acceptable level, to thus prevent defects such as short circuits or open circuits as the layers are built up.
The machinery to perform CMP has become highly sophisticated and efficient, with equipment costing millions of dollars. Nevertheless, there are some components of this equipment that require frequent replacement during the polishing operation, and are classed as consumables. These parts contribute significantly to the high costs of CMP equipment operation. One of these short-lived, consumable components is the retaining ring, which is part of the polishing head assembly (alternatively called the wafer carrier). The retaining ring serves to hold the semiconductor wafer and keep it in place during the polishing operation where it is forced against the polishing pad. The retaining ring conventionally consists of a stainless steel body to which a non-metallic wear member is attached. The non-metallic wear member surrounds the wafer, while the bottom surface of the wear member contacts the polishing pad directly. A flexible diaphragm within the polishing head above the wafer applies downward pressure on the wafer. Thus, the wafer is entrapped in a cavity created by the retaining ring assembly, the polishing pad below, and the flexible diaphragm above. Downward pressure on the retaining ring is applied independently of the flexible diaphragm, and can be varied in order to prevent the wafer from forcing its way out and being destroyed. The non-metallic part of the retaining ring is the only part that is in contact with the polishing pad in addition to the wafer. As such, it is subject to the polishing action of the polishing pad and the abrasive slurry.
Current retaining ring construction materials, although having other desirable properties, do not have good wear resistance. The average life of presently available retaining rings is approximately 500 wafers under normal circumstances. At increased temperature and pressure, this will be significantly lower. Replacement of the retaining ring on a regular basis adds substantially to the cost of ownership of the CMP process machinery. Under current practice, the entire retaining ring assembly is generally discarded and replaced with a new one. It would, therefore, be highly desirable to develop a retaining ring with increased useful life, with the capability of operating at increased temperatures and pressures, and which has the capacity of replacing only its wear-surfaces. One prior-art retaining ring currently available is manufactured of polyphenylene sulfide (PPS). This material seems satisfactory in most regards, but requires frequent replacement as the material wears. The typical lifetime of current designs is about 500 wafers.
In commonly-owned, copending application Ser. No. 10/087,223, filed on Mar. 1, 2002, which application is incorporated by reference herein, there is disclosed a polishing pad made of fibrous construction, which may include various natural or synthetic fillers, abrasives or friction modifiers, the whole matrix being bound together by a thermosetting resin, densified, and heat cured under pressure to produce a rigid, yet porous, structure. One or both surfaces of the polishing pad of the invention are ground, sanded, or the equivalent, to lift and expose fibers in a random, three-dimensional pattern that becomes the active polishing surface or surfaces. The basic fiber matrix may be any natural or synthetic fiber or blend thereof that is felted, dry laid, wet laid, woven, carded, spun, blown, or any other process that produces a porous fiber matrix that can be resin-impregnated and processed as above.